This invention relates to air cleaning, particularly involving a regenerable air cleaning device.
Confined areas that are subject to build-up of air-borne pollutants such as organic solvents or cigarette smoke can cause negative effects on the health of a person spending significant time in such an area. Cleaning of the air in the confined space, by filtration, absorption or adsorption of pollutants, reduces the possibility of these potentially negative effects being induced. However, the capacity of a filter or adsorbent diminishes as a result of use and ultimately saturation occurs. As a result, frequent replacement of saturated filters is necessary. This is inconvenient and costly. In addition, if a filter is integrated into ducting systems that move air into, out of or within a confined space, regular replacement of the integrated filter can be impractical.
French Patent Application No. 2,744,375 describes an activated charcoal filter integrated into ducting of a heating, ventilation and cooling (HVAC) system of an automobile. The activated charcoal filter is regenerated in situ by heat-induced desorption of adsorbed molecules. A fan then blows away the desorbed molecules. Thus, when the automobile""s electrical system is switched on, a control system automatically adjusts valves in the HVAC system to permit flow of air from outside the vehicle through the filter and again to the outside of the vehicle. A heat source, either integral with or in close proximity to the filter, is heated and the blowing fan is activated to cause air to flow through or over the filter to the outside of the vehicle. Heat causes material adsorbed on the filter to be released and the flow of air carries the released material to the outside of the vehicle. This sequence of events occurs for a predetermined time, regardless of the actual degree of contamination of the filter. It happens every time that the vehicle engine is started, and is not affected by the duration over which the engine is kept running. Hence the frequency and extent of regeneration are not related to the actual state of the filter, nor to the period of time over which the filter has been active.
Heating of the filter for regeneration puts additional strain on, and may necessitate additional capacity in, the automobile""s electrical system. The cooling effect of the blower, in operation to exhaust the desorbed molecules, puts a further demand on the electrical system to maintain a suitable regeneration temperature in the filter. This problem is particularly pronounced in the cold winters experienced in North America. Furthermore, during the predetermined regeneration time, the HVAC system is unable to perform its intended function of heating or cooling and ventilating. This is undesirable, especially in extreme weather conditions.
The filter of French Patent Application No. 2,744,375 is an integral part of an HVAC system of an automobile. It is not portable, and does not lend itself to retrofitting of existing automobiles that do not have such a filter as part of their HVAC systems. Retrofitting of existing vehicles would require significant labour and expense. This would be cost-prohibitive for many consumers.
U.S. Pat. No. 5,827,355 describes a regenerable carbon fiber composite filter. The composite material is rigid and comprises carbon fibers and a binder, such as powdered phenolic resin. The presence of the binder and the generally porous structure of the rigid filter result in a high current (1-20 amps) being required to heat the filter for regeneration purposes. The current flow is parallel to the pleats. Such an arrangement makes good electrical contact at the edge of the pleats difficult. The current flow, and hence heating of the filter, is expected to be uneven throughout the rigid structure due to the porosity of the structure and also due to the presence of the binder which can create regions of high resistance and consequent hot spots during regeneration.
Also disclosed in U.S. Pat. No. 5,827,355 is an air conditioner that includes the rigid composite air filter. The air conditioner is designed for mounting in a wall and connection to outside air. Positioning of a movable damper selects either fresh outside air or recirculated air from the interior of the room, or both. A first blower is provided to pass air to be treated over the filter and into the room. When in regeneration mode, the filter is heated and the damper is positioned to direct air, moved by a second blower over the heated filter, through an exhaust outlet. As discussed above, blowing air during regeneration is not desired due to the cooling effect of air movement. The device of U.S. Pat. No. 5,827,355, having two blowers and a moving damper providing multiple air paths, is cumbersome and will be more prone to mechanical failure than a device having fewer such parts.
What has not been appreciated until now, with respect to activated carbon filters, is the critical effect that an integrated system for controlling cycles of filtering and regeneration of activated carbon has on the performance and longevity of such filters.
In one aspect, the present invention provides a regenerable air cleaning device comprising:
a filter holder supporting a regenerable filter that includes activated carbon fibers (ACF); and
a control system that is adapted to determine when to regenerate the regenerable filter.
The device is preferably a regenerable air cleaning device wherein the filter holder and filter are integral and non-demountable and the device further comprises a heat source for regenerating the regenerable filter, although also considered is a regenerable air cleaning device in which the filter holder and filter are demountable so that the filter can be removed for regeneration by a heat source and then remounted.
The device can further comprise:
a housing having an air inlet port and an air outlet port in communication to provide a passage for air to pass through the housing, the filter being situated in the passage; and
a fan situated in the passage to draw air through the housing;
whereby, in operation, the filter removes contaminants from air drawn through the housing.
In another aspect, the present invention provides a method of cleaning air in a confined space, comprising operating the regenerable air cleaning device disclosed herein in the confined space.
An advantage of the filter/control system combination of the present invention is that the filter exhibits high performance and longevity over many regeneration cycles, in some instances more than 50. The life of the filter will be equal to, or greater than, the life of the other components of the device.
In its simplest embodiment, the filter/control system combination of the present invention can be adapted for use, for example, in a range hood over a cooking stove. Such an embodiment would require only a filter in a filter holder and an integrated control system, with each being adapted for connection to a suitable power supply.
The present invention also provides an air cleaning device that comprises the filter/control system combination and that can be stand-alone. It can operate independently of, or integrated within, an HVAC system, such as found in automobiles and other vehicles such as an aircraft, boat and the like. It may also be used in non-vehicular applications, for instance, cleaning the air in places such as a restaurant, commercial kitchen, clean room, operating theatre, laboratory, house, garage, factory, rest room or office.
More generally, it may be used in any residential, commercial or other building that may be subjected to build-up of vapours, gases or odours produced, for example, directly or indirectly by human or animal occupants (e.g. cigarette smoke, paints and coatings odours, etc.).
A stand-alone device of the invention containing the filter/control system combination can be sized for portability and for various applications, including placement within a confined space such as the cabin of a motor vehicle. A device of the invention that is designed for an automobile can be powered by the vehicle""s 12V power port (lighter socket) or a 12V AC adapter. In such a configuration, it can operate simultaneously with the vehicle""s HVAC system. Such a device can be simple in construction, having a single blower or fan and one air passage, with no need for moving parts such as dampers or valves. It has low power requirements and does not put significant extra load on the electrical system of a vehicle. Consequently, no additional capacity in, or modification to, the electrical system is required.